Piston engine comprising member to cover bottom face of valve head of poppet valve

ABSTRACT

To achieve high compression ratio and lower temperature of the exhaust poppet valve in an engine provided with a poppet valve on an extend part of a combustion chamber outside a main cylinder, disclosed is a valve cover having a cylindrical side face and upper face, an compression ring either the cylindrical side face and an inner wall of the sub cylinder, means to contact closely a bottom face of a poppet valve and the upper face of the valve cover, the upper part of the valve cover occupying most part of the combustion chamber facing with the bottom face, the valve cover moves along with the poppet valve when the poppet valve is lifted, a combination of overhead valves and the poppet valve including one intake valve and one exhaust valve, and total number of the overhead valve and poppet valve is not less than 3.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a piston engine comprising a member to cover a bottom face of a valve head of a poppet valve. When the combustion chamber extends outside the main cylinder, the member occupies a space facing with the bottom face of the poppet valve provided outside a main cylinder in a combustion chamber.

2. Description of the Related Art

The suction resistance and exhaust resistance of a four cycle engine are high when it rotates at high speed. The suction lifts in this engine are extremely small in the initial stages of the periods when the suction valve is open. The initial stages are shorter when the engine rotates at a higher speed. This restricts the inflow of suction gas. As a result, in the initial stages of the periods when the suction valve is open, the pressure in the cylinder is lower than the pressure at the back of the piston.

Under this condition, the piston keeps moving downward against the pressure on it. As a result, the negative work increases. This increases the loss caused by the suction resistance, so that the torque lowers.

FIG. 14 shows the engine performance curves shown on page 90 of No. 434 issued in November, 1995 of a magazine entitled “Internal Combustion Engine” published by Sankaido. With reference to FIG. 14, the torque of a four cycle engine is lower than the maximum torque points L1 and L2 on torque curves when the engines rotate at speeds higher than those for these points.

The exhaust lifts in a four cycle engine are extremely smaller in the initial stage of the period when the exhaust valve is open until the piston reaches the bottom dead point of each exhaust stroke than in the middle stage of this period. Consequently, when the engine rotates at high speed, the pressure created in the cylinder when the piston is at the bottom dead point is high. As a result, just after the piston leaves the bottom dead point, the exhaust resistance causes a great loss.

FIG. 15 shows the side valve engine disclosed in Patent document 1. The main combustion chamber 127 of this engine has an extension outside the cylinder. This makes it possible to fit another suction valve and another exhaust valve that face the top of the piston.

The space between the suction and exhaust valves is narrowed to make the combustion chamber compact in Patent document 1.

However, the volume of the main combustion chamber is increased by the space between the wall fitted with a side valve and the surface facing the wall. The volume of this space increases with the lift of the side valve. Consequently, the combustion chamber having a suction valve facing the top of the piston and a side valve cannot have a high combustion ratio, so that the engine efficiency is low.

FIG. 17 shows a side valve engine described in patent document 3. In FIG. 17, there is a space of a combustion chamber between an edge of a guide hole facing with the combustion chamber and a valve sheet for the intake valve. According to FIG. 17, the combustion chamber extends outside the volume changing member 117 in a view observing from the central axis of the cylinder toward the volume changing member. The volume of the combustion chamber increases by this extended portion.

Reference numeral 118 denotes the guide hole. Reference numeral 113 denotes the intake valve. Reference numeral 117 denotes the volume changing member. Reference numeral 127 denotes the combustion chamber.

The side valve internal combustion engine of patent document 3 is provided with a pair of an intake and exhaust valves provided at the lateral periphery of the cylinder. Therefore, the total area of the pair of intake and exhaust valves of the side valve internal combustion engine of patent document 3 is smaller than that of an engine provided with four valves at a wall facing with an upper face of a piston in the wall of the combustion chamber.

In the side valve internal combustion engine of patent document 3, a part protruding into the combustion chamber of the volume changing member is heated to high temperature by the combustion gas while the intake valve is closed.

Combustion occurs intermittently in a piston engine. An inner wall of a combustion chamber is cooled by intake gas in a piston engine. In a spark-ignition engine, mixture gas thus forms a quench zone along with an inner wall of a combustion chamber. This quench zone prevents high heat from flowing to the inner wall of the combustion chamber.

When the exhaust poppet valve opens, both a bottom face of a valve head of the exhaust poppet valve and an upper face facing with a gas passage of the valve head are exposed to the combustion gas. The temperature of the exhaust poppet valve thus gets high. When the piston is under high load, the quench zone is poorly formed along with the bottom face of the valve head of the exhaust poppet valve. Therefore, the mixture zone along with the bottom face self-ignites. When the amount of self-ignited mixture increases, the quench zone is broken also at a part facing with the inner wall of the combustion chamber other than the bottom face. As a result, knocking occurs.

FIG. 16 shows the engine of patent document 2.

When the sliding valve shown in the third aspect of patent document 2 is used as an exhaust valve, both upper and lower faces of a first compression ring of the sliding valve are exposed to the combustion gas at the beginning of exhaust strokes. Reference numeral 8 denotes the first compression ring. Thus, the first compression ring is heated to the ignition temperature of the lubricant or more. The first compression ring is then seized up. The engine of Japanese patent application No. 2008-120801 comprises a sub cylinder outside the main cylinder.

If the strokes of the piston are longer than its diameter, the combustion gas conversion efficiency is high, but the suction efficiency is low when the engine rotates at high speed. The low suction efficiency leads to low torque. If the piston strokes are shorter than the piston diameter, the suction efficiency is high when the engine rotates at high speed, but the combustion gas conversion efficiency is low.

Therefore, long strokes of the pistons of conventional spark ignition engines have been incompatible with torque increases that may be caused when the engines rotate at high speed.

Patent document 1: Japanese Patent Application Publication No. 2000-282814 (JP2000-282814A)

Patent Document 2: Japanese Patent Application No. 2008-120801, Japanese Patent No. 4230529

Patent document 3: Japanese Patent Application Publication No. 2001-355470

SUMMARY OF THE INVENTION

A first object is to raise compression ratio of an engine which comprises a valve on a wall of an extended part of a combustion chamber outside a main cylinder.

A second object is to lower a temperature of the valve when it is used as an exhaust valve.

A third object is to improve fuel efficiency of a piston engine.

Hereinafter described is a structure of a piston engine according to a first aspect of the present invention.

The piston engine of the present invention comprises a cylinder head, a cylinder block, a main cylinder, a piston, a sub cylinder, an overhead valve and a poppet valve. A member to cover a bottom face of a valve head of the poppet valve is provided.

The piston reciprocates in the main cylinder. A combustion chamber is defined between the piston and the cylinder head. The combustion chamber further extends outside the main cylinder. An inner wall of the combustion chamber comprises a first part and a second part. The first part represents a part of the inner wall which faces with an upper face of the piston. The second part represents the inner wall of an extended part outside the main cylinder. The sub cylinder is provided outside the main cylinder.

The poppet valve is provided on the second part of the inner wall. The poppet valve is provided with a second drive unit to drive a stem of the poppet valve. When the poppet valve is open, gas passes through between the poppet valve and a second valve sheet of the poppet valve.

The member reciprocates in the sub cylinder, and includes a cylindrical side face.

The valve head positions between the second valve sheet and the member.

Means to contact the second valve sheet, the member and the valve head intimately with one another is provided. The means may be a combination of the poppet valve integrally formed with the member and a device to shift the member toward the second valve sheet, or may be a device to bias the member toward the second valve sheet.

The device to shift the member toward the second valve sheet may be one of a third spring provided with abutting the member, a pneumatic unit provided with abutting the member, a hydraulic unit provided with abutting the member and a second spring provided with abutting the stem of the poppet valve.

The device to bias the member toward the second valve sheet may be one of a third spring provided with abutting the member, a pneumatic unit provided with abutting the member and a hydraulic unit provided with abutting the member.

The second drive unit and the means drive the poppet valve and the member integrally.

A compression ring is provided at a position wedged between an inner wall of the sub cylinder and the cylindrical side face of the member.

The member is located with abutting the bottom face of the poppet valve.

The overhead valve is provided on the first part of the inner wall. The overhead valve is provided with a spring and a first drive unit. When the overhead valve is open, gas passes through between the overhead valve and a valve sheet of the overhead valve. When the poppet valve is open, gas passes through between the poppet valve and a second valve sheet of the poppet valve. The gas is either intake gas flowing into the combustion chamber or combustion gas flowing out from the combustion chamber.

A combination of the overhead valve and the poppet valve includes at least one intake valve and one exhaust valve.

The total number of the overhead valve and poppet valve is not less than 3.

About a structure of a piston engine according to a second aspect of the present invention, only the difference from the first aspect is described below.

The sub cylinder is provided at a position where one end thereof is located adjacent to the second valve sheet.

The whole circumference of the cylindrical side face of the member adjacent to the poppet valve is sectioned into two half circumferences by a line which is perpendicular to a line connecting the central axis of the main cylinder to the central axis of the sub cylinder intersecting at the central axis of the sub cylinder.

The two half circumferences are referred to as a first half circumference which is close to the central axis of the main cylinder and a second half circumference which is away from the central axis of the main cylinder.

The cylindrical side face of the member adjacent to the poppet valve is sectioned into two half surrounding faces. The two half surrounding faces are a first half surrounding face having the first half circumference and a second half surrounding face having the second half circumference.

A part adjacent to the second valve sheet of the sub cylinder faces with the second half surrounding face.

A fixed wall, which is located outside the combustion chamber extended outside the main cylinder, is formed adjacent to the inner wall facing with the second half surrounding face of the sub cylinder.

An opening of the sub cylinder is provided in the vicinity of the one end of the sub cylinder.

A first gas path is provided between the second valve sheet and outside of the engine. A second gas path is provided which communicates a space inside the main cylinder and the first gas path in a short distance when the poppet valve is open, and the second gas path includes the opening.

The opening faces with the first half surrounding face.

According to the piston engine of the second aspect, the area heated by the combustion gas is reduced in the cylindrical side face of the valve cover 7 compared to that of the engine of patent document 3, and thus the amount of thermal loss is reduced in this engine. As a result, the third object is achieved in the second aspect.

About a structure of a piston engine according to a third aspect of the present invention, only the difference from the first aspect is described below.

According to the engines of the first and second aspects, a stroke length of the piston is not shorter than a diameter of the piston.

According to the piston engine of the third aspect conversion efficiency of the combustion gas is improved compared to short stroke engines. Also, decrease of intake efficiency is improved, which occurs in long stroke engines rotating at high speed. As a result, it becomes possible to strike the improvement of conversion efficiency and increase of torque in balance. Thus, the third object is achieved in the third aspect.

The piston engines according to the three aspects of the present invention may be spark-ignition engines or compression-ignition engines, and the spark-ignition engines may be 2-stroke engines or 4-stroke-engines. When the engine of the invention is a spark-ignition engine, a spark plug may be provided anywhere on the wall of the combustion chamber.

According to the engines of the three aspects of the present invention, the volume of the combustion chamber reduces by the volume of an upper part of the member which protrudes into the space in the combustion chamber which would face with the closed poppet valve if the member were not provided. Therefore, the engines can achieve high compression ratio of the combustion chamber. Thus, the first object is achieved.

Further, a total area of the intake and exhaust valves of the engine according to the three aspects of the present invention is larger than engines provided with overhead valves only in a main cylinder. Therefore, intake and exhaust resistance reduces especially when rotating at high speed. Output power of the engine of the invention thus can increase.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 3 are views showing the first embodiment, wherein:

FIG. 2 is a view when the poppet valve is open.

FIGS. 4 to 7 are views showing modifications of the first embodiment.

FIGS. 8 and 9 are views showing the second embodiment.

FIGS. 10 to 13 are views showing embodiments to improve the first to fifth embodiments.

FIGS. 14 to 17 are views showing prior art, wherein:

FIG. 14 is a graph showing power output and torque of the 3RZ-FE engine and 22R-E engine;

FIG. 15 is a view of the combustion chamber of Japanese patent application publication No. 2000-282814;

FIG. 16 is a view of the engine according to the third aspect of Japanese patent application No. 2008-120801; and

FIG. 17 is FIG. 2 of Japanese patent application publication No. 2001-355470.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A first embodiment will be described.

The first embodiment is included in the first aspect.

A piston engine shown in FIGS. 1 and 2 comprises a cylinder head 5, a cylinder block 6, a main cylinder 1, a piston 26, a sub cylinder 4, overhead valves 25A and 25B, and a poppet valve 2.

The piston 26 reciprocates in the main cylinder 1. A combustion chamber 27 is defined between the cylinder head 5 and the piston 26. The combustion chamber 27 further extends outside the main cylinder 1. An inner wall of the combustion chamber 27 comprises a first part and a second part. The first part represents the inner wall which faces with an upper face of the piston 26. The second part represents the inner wall of the extended part outside the main cylinder 1.

The combustion chamber 27 may extend both right and left sides outside the main cylinder 1.

The sub cylinder 4 is installed in the cylinder block 6 which locates outside the main cylinder 1.

The overhead valves 25A and 25B are provided in the first part which faces with the upper face of the piston 26. When the overhead valves 25A and 25B are open, gas passes through gaps between the overhead valves 25A and 25B and valve sheets of them.

The overhead valves 25A and 25B are provided with springs 29A and 29B respectively. The overhead valves 25A and 25B are respectively provided with cams 28A and 28B as a first drive unit to lift the overhead valves 25A and 25B.

When the overhead valve 25A is configured as an intake valve and the overhead valve 25B is configured as an exhaust valve, the overhead valve 25A opens by the cam 28A during an intake stroke of the piston 26 and the overhead valve 25B opens by the cam 28B during an exhaust stroke of the piston 26.

The cams 28A and 28B of the overhead valves 25A and 25B may be replaced with electromagnetic units or hydraulic units.

The poppet valve 2 is provided on the second part extended outside the main cylinder 1. A plurality of poppet valves 2 may be provided in the second part. A bottom face 3 of the poppet valve 2 denotes a bottom face of a valve head of the poppet valve 2. At the periphery of an upper face of the valve head, the poppet valve 2 has a face which intimately contacts with a second valve sheet 16 of the poppet valve 2 when the poppet valve 2 is closed. An opening is provided inside the second valve sheet 16 of the poppet valve 2, and the opening communicates to outside of the engine. When the poppet valve 2 is closed, the valve head of the poppet valve 2 positions at the opening. The poppet valve 2 is provided with a cam 30 which abuts the poppet valve 2.

When the poppet valve 2 is open, intake or exhaust gas passes though a gap between the poppet valve 2 and the second valve sheet 16. That is, the poppet valve 2 can be used as either an intake valve or an exhaust valve.

When the poppet valve 2 is used as an intake valve, it opens by the cam 30 during an suction stroke of the piston 26.

When the poppet valve 2 is used as an exhaust valve, it opens by the cam 30 during an exhaust stroke of the piston 26.

The cam 30 functions as a second drive unit to lift the poppet valve 2.

The cam 30 of the poppet valve 2 may be replaced with an electromagnetic unit or a hydraulic unit.

Three examples of providing the intake and exhaust valves will be described. The three examples relate to the overhead valves 25A and 25B and poppet valve 2.

The features shown in the three examples are not disclosed in patent document 3.

In the three examples, the total number of the overhead valve and the poppet valve is not less than 3.

In the first example, a plurality of exhaust poppet valves are provided on the second part, and the poppet valves provided on the second part are limited to exhaust poppet valves. This feature is not disclosed in patent document 3. At least one overhead intake valve is provided on the first part.

Therefore, in the first example, it becomes possible to increase the number and the area of the exhaust poppet valves provided on the second part compared to the engines of patent documents 1 and 3.

When the exhaust poppet valves are open, the bottom faces 3 are covered with the upper face 8 of the valve cover 7 described below and the bottom faces 3 do not contact with the combustion gas. The temperature of the exhaust poppet valves thus does not rise high compared to the exhaust valve of the patent document 1. It is possible to lower the temperature of only the exhaust poppet valves provided on the second part. Therefore, the second object is partly achieved in this engine.

The upper and lower faces of the compression ring 9 are not exposed to the combustion gas at a time. Therefore, the temperature of the compression ring 9 does not rise high compared to the third aspect of patent document 2 where the sliding valve is used as an exhaust valve.

In the first example, the amount of the combustion gas passing through each poppet valve provided on the second part is reduced compared to the exhaust poppet valve of patent document 3, and the highest temperature of the plurality of exhaust poppet valves becomes lower. Therefore, resistance to knocking of the first example is improved compared to patent document 3.

The second example will be described.

A plurality of intake poppet valves are provided on the second part, and the poppet valves provided on the second part is limited to intake valves. This feature is not disclosed in patent document 3. At least one exhaust overhead valve is provided on the first part. Therefore, in the second example, it becomes possible to increase the number and the area of the intake valves compared to the engines of patent documents 1 and 3.

The third example will be described with reference to FIG. 3.

One or more overhead valve is provided on the first part of the inner wall of the combustion chamber 27, and all overhead valve provided in the first part is the intake poppet valve 33. The exhaust poppet valve 34 is provided on the second part extended outside the main cylinder 1. It becomes possible to prevent the temperature of the exhaust poppet valve 34 from rising high according to the same ground described in the first example for explaining the temperature of the exhaust poppet valves. The exhaust valve 34 does not lower filling rate of intake. Therefore, the second object is perfectly achieved in this engine. The temperature of the intake valve 33 does not rise high.

According to this feature, the wall of the combustion chamber does not have in any part a higher temperature than the exhaust valves described in the description of the related art. Therefore, when the piston is under a high load, a quench zone is formed along with the entire wall of the combustion chamber.

As a result, in the case of a spark-ignition engine, resistance to knocking is improved compared to the engines of patent documents 1 and 3. Then, it becomes possible to increase a compression ratio of this engine, and thermal efficiency of this engine is thus improved. Therefore, the third object is achieved in this engine.

Piston engines can operate at least with a combination of one intake valve and one exhaust valve. Therefore, when a combination of the overhead valves 25A and 25B and poppet valve 2 includes at least one intake valve and one exhaust valve, the piston engine of the first embodiment can operate whether the other valve than the combination is configured as an intake valve or an exhaust valve.

The total number of the overhead valves and the poppet valve is not less than 3.

It is described that the embodiment comprises the two overhead valves 25A and 25B. However, when the total number of the overhead valve and poppet valve is not less than 3, the number of the overhead valve may be any number more than one. Also, when the total number of the overhead valve and poppet valve is not less than 3, the configuration of intake and exhaust valves may be modified differently from the above three examples.

The piston engine of the first embodiment comprises a valve cover 7.

The valve cover 7 reciprocates in the sub cylinder 4. The valve cover 7 covers the bottom face 3 of the poppet valve 2. The valve cover 7 positions with its upper part being protruded into an inner space of the combustion chamber 27.

The valve cover 7 comprises a cylindrical side face, an upper face and a back face. The back face abuts a spring 12. A lower part of the cylindrical side face faces with an inner wall of the sub cylinder 4.

The valve cover 7 and poppet valve 2 are driven by the cam 30 which lifts the poppet valve 2. The cam 30 functions as a second drive unit.

A central axis of a stem of the poppet valve 2 is identical to or approximately parallel to a central axis of the sub cylinder 4. Therefore, when the cam 30 lifts the poppet valve 2, the valve cover 7 moves along with the poppet valve 2 and the lower part of the valve cover 7 accordingly moves inside the sub cylinder 4. Therefore, the cam 30 of the poppet valve 2 also functions as a drive unit to lift the valve cover 7.

A space is defined between the valve sheet 16 of the poppet valve 2 and an upper end 10 of the sub cylinder 4. The upper end 10 faces with the space of the combustion chamber 27.

A ring groove for a compression ring 9 is provided on the cylindrical side face of the valve cover 7. The compression ring 9 is disposed to this ring groove. This feature is not shown in patent document 3.

When the poppet valve 2 is closed, the compression ring 9 is wedged between the inner wall of the sub cylinder 4 and the ring groove. Since the compression ring 9 is wedged between the inner wall of the sub cylinder 4 and the cylindrical side face of the valve cover 7 when the poppet valve 2 is closed, the combustion chamber 27 is sealed with the compression ring 9 so that combustion gas does not leak from the combustion chamber 27 through the gap between the valve cover 7 and the inner wall of the sub cylinder 4 into a space where the valve cover 7 does not occupy in the sub cylinder 4.

A spring 12 for the valve cover 7 is provided with abutting the back face of the valve cover 7, in order that the upper face 8 of the valve cover 7 intimately contacts with the bottom face 3 of the poppet valve 2. The spring 12 biases the valve cover 7 to let it abut the bottom face 3 of the poppet valve 2. The valve cover 7 and poppet valve 2 are consequently driven integrally by the cam 30 and spring 12.

The spring 12 is one of means to let the second valve sheet 16, poppet valve 2 and valve cover 7 contact intimately with one another.

The spring 12 biases the valve cover 7 toward the second valve sheet 16.

The spring 12 also functions as a valve spring of the poppet valve 2 which may be provided with abutting the poppet valve 2. In the embodiment shown in FIG. 1, the valve spring in contact with the poppet valve 2 is not provided. By providing the spring 12 for the valve cover 7, the valve spring abutting the poppet valve 2 can be omitted. That is, the valve spring abutting the stem of the poppet valve 2 is not essential. As a matter of course, the valve spring abutting the stem of the poppet valve 2 may be further provided.

While the piston is in compression and combustion strokes, combustion gas flows toward the ring groove through the gap between the cylindrical side face of the valve cover 7 and the inner wall of the sub cylinder 4. The combustion gas flows in one direction. Then, the compression ring 9 is subjected to a force in the direction to compress the spring 12. Accordingly, the combustion gas blows the valve cover 7. Therefore, it is necessary that the spring 12 is stronger than the combustion gas pressure applied to the compression ring 9.

The valve cover 7 is not driven when the poppet valve 2 is closed. The valve cover 7 thus does not move while the piston is in a combustion stroke. As a result, the valve cover 7 is hard to seize up.

In FIG. 1, the upper face 8 of the valve cover 7 and the bottom face 3 of the poppet valve 2 are in intimate contact with each other, and a boundary of the valve cover 7 and poppet valve 2 is drawn by a solid line. In FIG. 1, two lead lines refer the solid line showing the intimate contact. The upper lead line is for reference numeral 8 and the lower one is for reference numeral 3. The solid line represents both the upper face of the valve cover 7 and the bottom face 3 of the poppet valve 2. Therefore, the two lead lines are drawn in the opposite direction with each other.

When the upper face 8 of the valve cover 7 and the bottom face 3 of the poppet valve 2 are in intimate contact with each other, combustion gas does not break into the boundary between the valve cover 7 and the bottom face 3 of the poppet valve 2. It is preferable that the upper face 8 of the valve cover 7 and the bottom face of the poppet valve 2 have the same size. In this case, the upper face 8 of the valve cover 7 is not subjected to combustion gas pressure. If the upper face 8 of the valve cover 7 is larger than the bottom face 3 of the poppet valve 2, the upper face 8 of the valve cover 7 is subjected to the combustion gas pressure.

The poppet valve 2 is closed during a compression stroke of the piston 26. The valve cover 7 is located with abutting the bottom face 3 of the poppet valve 2. The upper part of the valve cover 7 occupies the most space of the extended part of the combustion chamber 27 outside the main cylinder 1, which would face with the bottom face 3 of the poppet valve 2 if the valve cover 7 were not provided. As a result, the volume of the combustion chamber 27 reduces by the volume of the upper part of the valve cover 7 which protrudes into the combustion chamber 27. Compared to the engine of patent document 1, compression ratio of the combustion chamber 17 becomes high. Therefore, the first object is achieved by this engine.

Regarding FIG. 2, when the cam 30 lifts the poppet valve 2, the valve cover 7 moves along with the poppet valve 2. When the poppet valve 2 lifts to the maximum, the most part of the valve cover 7 positions inside the sub cylinder 4. When the poppet valve 2 is open, the combustion chamber 27 facing with the upper face of the piston communicates to outside of the engine.

In the first embodiment, the poppet valve 2 is provided on the wall of the first part extended outside the main cylinder 1 of the combustion chamber 27. Further, the total number of the overhead valves and poppet valve is not less than three. Therefore in the engine of first embodiment, the total area of the intake and exhaust valves increases compared to the conventional art which does not have a poppet valve outside a main cylinder. In the first embodiment, the overhead valves 25A and 25B face with the upper face of the piston. Therefore in the engine of the first embodiment, the total area of the intake and exhaust valves increases compared to the side valve engine of patent document 3.

Therefore, when the engine of the first embodiment rotates at high speed, efficiency of intake and exhaust increases compared to the conventional art. This advantage is not disclosed in patent documents 1 and 3.

It is not disclosed in patent document 3 to increase the area of intake or exhaust side valves.

It is disclosed in patent document 2 to provide both overhead valve and sliding valve. However, this feature is different from the first embodiment.

Second to fifth embodiments are modifications of the first embodiment. The first object is achieved in these embodiments.

For these embodiments, only the difference from the first embodiment will be described.

The second embodiment will be described.

In FIG. 4, the sub cylinder 4 is provided in the cylinder head 5. In this case, the gas path contacting with the poppet valve 2 is provided in the cylinder block. The poppet valve 2 provided outside the cylinder is a side valve.

The third embodiment will be described.

In FIG. 5, a pneumatic unit, hydraulic unit 19, electromagnetic unit or electric unit is employed in place of the spring 12. These units bias the valve cover 7 so that the upper face 8 presses the bottom face of the poppet valve 2. These units and the third spring 12 are to bias the valve cover 7 toward the valve sheet 16.

In FIG. 5, the compression ring 9 is subject to the pressure of the combustion gas so that the valve cover is pushed downwards. The valve cover and the bottom face of the poppet valve are not separated from each other by the pressing force.

The above-described units including the hydraulic unit 19 bias the valve cover toward the valve sheet 16 of the poppet valve 2 with a force not less than this pressing force.

The fourth embodiment will be described.

In FIG. 6, the poppet valve 2 and valve cover 7 are integrally formed.

In FIG. 6, a dashed dotted line shows a phantom joint face between the poppet valve 2 and valve cover 7. Actually, the joint face shown by the dashed-dotted line does not exist.

In FIG. 6, when the third spring 12 to push the valve cover 7 is not provided, the second spring 31 abutting the stem of the poppet valve 2 functions as a replacement of the third spring 12. The second spring 31 pulls the poppet valve 2. The spring 12 may be thus omitted.

Conversely, when the third spring 12 is provided, the second spring 31 abutting the stem of poppet valve 2 may be omitted.

The fifth embodiment will be described.

In FIG. 7, a ring groove for the compression ring 9 is provided on an inner wall of the sub cylinder 4. The compression ring 9 is disposed onto the ring groove.

In order that the compression ring 9 seals the combustion gas, the compression ring 9 is wedged between the cylindrical side face of the valve cover 7 and the inner wall of the sub cylinder 4. A ring groove is not provided on the cylindrical side face of the valve cover 7. Therefore in this engine, the force of the combustion gas given to the compression ring 9 does not push the valve cover 7 downward. Therefore in the engine shown in FIG. 7, a weaker spring may be employed than the spring of the engine shown in FIG. 1.

The following sixth to tenth embodiments show additional features to the first to fifth embodiments. The sixth to tenth embodiments are to further modify the first to fifth embodiments.

The sixth to tenth embodiments are not disclosed in patent documents 1 and 3.

The sixth and eighth to tenth embodiments are not disclosed in patent document 2.

The sixth embodiment will be described with reference to FIGS. 8 and 9.

The sixth embodiment is included in the second aspect.

The end 10 of the sub cylinder 4 is disposed at a position adjacent to the second valve sheet 16 of the poppet valve 2. The part adjacent to the poppet valve 2 of the sub cylinder 4 may be formed integrally with the part facing with the compression ring 9 of the sub cylinder 4, or may be formed as a part of the cylinder head. When the poppet valve 2 is open, the valve head of the poppet valve 2 is located inside the sub cylinder 4.

The whole circumference of the cylindrical side face of the valve cover 7 adjacent to the poppet valve 2 is sectioned into two half circumferences by a dashed-four dotted line 38 which is perpendicular to a dashed-three dotted line 39 connecting the central axis 37 of the main cylinder 1 and the central axis of the sub cylinder 4 intersecting at the central axis of the sub cylinder 4.

The two half circumferences are referred to as a first half circumference which is close to the central axis 37 of the main cylinder 1 and a second half circumference which is away from the central axis 37 of the main cylinder 1.

The cylindrical side face of the valve cover 7 adjacent to the poppet valve 2 is sectioned into two half surrounding faces. The two half surrounding faces are a first half surrounding face 40 having the first half circumference and a second half surrounding face 35 having the second half circumference.

A part adjacent to the second valve sheet of the sub cylinder 4 faces with the second half surrounding face 35. The part is drawn as the sub cylinder referred by reference numeral 4 in FIG. 9.

A fixed wall, which is located outside the combustion chamber extended outside the main cylinder 1, is provided adjacent to the inner wall facing with the second half surrounding face 35 of the sub cylinder 4.

When the part adjacent to the poppet valve 2 of the sub cylinder 4 is formed integrally with a part facing with the compression ring 9 of the sub cylinder 4, the fixed wall located outside the combustion chamber extended outside the main cylinder 1 is constituted by a fixed wall which is adjacent to the outer face 36 facing with the second half surrounding face 35 of the sub cylinder 4 and the sub cylinder 4 which faces with the second half surrounding face 35.

An opening 18 of the sub cylinder 4 is provided in the vicinity of the one end 10 of the sub cylinder 4.

A first gas path 11 is provided between the second valve sheet 16 of the poppet valve 2 and outside of the engine.

A second gas path 21 is provided which communicates the space inside the main cylinder 1 and the first gas path 11 in a short distance when the poppet valve 2 is open. The opening 18 constitutes the second gas path 21. In FIG. 9, the opening 18 is shown by a dashed-two dotted line.

The opening 18 faces with the first half surrounding face 40.

The second gas path 21 is included in the combustion chamber surrounded by the second part.

A plurality of the combinations of the valve cover 7, sub cylinder 4 and the opening 18 may be provided in the second part which extends outside the main cylinder 1.

In the sixth embodiment, the volume of the combustion chamber extended outside the main cylinder is decreased compared to the engines disclosed in patent documents 1 and 3, and the compression ratio is thus high.

The cylindrical side face of the valve cover 7 is subject to the heat of the combustion gas in a part of its upper part during combustion strokes and expansion strokes.

A part adjacent to the poppet valve 2 of the cylindrical side face of the valve cover 7 is subject to the pressure of the combustion gas in a direction from the central axis of the main cylinder 1 to the central axis of the sub cylinder 4 during combustion strokes and expansion strokes. When the part adjacent to the poppet valve 2 of the cylindrical side face of the valve cover 7 is divided into two sections, the second half surrounding face 35 is pressed to and contacts closely with the part of the sub cylinder 4 comprising the outer face 36. The part comprising the outer face 36 of the sub cylinder 4 faces with the second half surrounding face 35. The combustion gas does not flow in between the contacted two faces. The heat of the combustion gas does not flow into the contacted two faces.

Consequently in the sixth embodiment, the area which is subjected to the heat of the combustion gas in the cylindrical side face of the valve cover 7 is reduced compared to the engine disclosed in patent document 3, and the thermal loss of this engine is thus reduced. The larger the area in close contact is, the lower the temperature of the cylindrical side face becomes. Therefore, the fuel efficiency is improved and the resistance to knocking is also improved compared to the engine disclosed in patent document 3.

The seventh embodiment will be described.

The seventh embodiment is included in the third aspect.

The problems relating to a balance of conversion efficiency improvement and torque enhancement is described in the description of the related art.

This problem can be solved by the following feature. The engines of the first to sixth embodiments are further configured such that the length of the piston stroke is not shorter than the diameter of the piston. That is, the length of the piston stroke is approximately same as or longer than the diameter of the main piston in these engines.

By this feature, the conversion efficiency of combustion gas is improved compared to short stroke engines. Also, decrease of intake efficiency which occurs in long stroke engines rotating at high speed is improved. As a result, it becomes possible to strike improvement of conversion efficiency and increase of torque at high speed in balance. The third object is thus achieved.

The eighth embodiment will be described with reference to FIG. 10.

The part adjacent to the poppet valve 2 of the valve cover 7 is heated by the combustion gas in combustion strokes. In the case of a spark-ignition engine, knocking is caused by a high temperature part in a combustion chamber. In the case of a piston engine, a filling rate of intake decreases due to a high temperature part in a combustion chamber.

In order to solve these problems, a spray valve 41 is further provided to the engines of the first to seventh embodiments. The spray valve 41 sprays oil to the back face of the part adjacent to the poppet valve 2 of the valve cover 7. Further, the spring 12 is provided with abutting the back face. Thus, the temperature of the part adjacent to the poppet valve 2 of the valve cover 7 becomes low, and knocking occurs less. Then, it becomes possible to configure the compression ratio higher, and the heat efficiency is thus improved. As a result, the third object is achieved.

Further, the filling rate of intake does not decrease.

The ninth embodiment will be described.

The following feature of the engine shown in FIG. 11 may be added to any embodiments except the fourth embodiment.

The face abutting the poppet valve 2 of the valve cover 7 is a convex curve, and the face contacting with the valve cover 7 of the poppet valve 2 is a concave curve. These two faces have a same curvature.

In the engine shown in FIG. 1, if the pressure in the combustion chamber increases sharply, the part adjacent to the poppet valve of the valve cover 7 is pressed in a direction toward the opposite side of the piston 26. The part adjacent to the poppet valve 2 of the valve cover 7 may be thus deformed. The bottom 3 of the poppet valve 2 is not deformed. On the other hand, a gap does not formed between the two curved faces in the engine shown in FIG. 11. A solid line shows the state that the two faces closely contacted with each other. Even if the pressure in the combustion chamber increases sharply, the two faces shown in FIG. 11 do not separate from each other.

The tenth embodiment will be described.

In the engine shown in FIG. 7, when oil is supplied to the inner wall of the sub cylinder 4, the oil penetrates into the gap between the cylindrical side face of the valve cover 7 and the inner wall of the sub cylinder 4 by capillarity and movement of the valve cover 7. The oil penetrated into the gap is sucked into the combustion chamber during intake strokes. As a result, oil consumption increases.

On the other hand, when an oil ring 22 is provided on the cylindrical side face of the valve cover 7 as shown in FIG. 12, the oil consumption can be controlled. However, the compression ring 9 provided on the inner wall of the sub cylinder does not move. Accordingly, the compression ring 9 does not transfer the oil. Therefore, in the case shown in FIG. 12, the compression ring 9 provided at the closer side to the combustion chamber lacks its lubrication.

This problem is solved by adding the following feature.

As shown in FIG. 13, the upper compression ring 23 is provided on the inner wall of the sub cylinder at the closer side to the combustion chamber 27, and the lower compression ring 24 is provided on the cylindrical side face of the valve cover 7. The upper compression ring 23 is provided between the lower compression ring 24 and combustion chamber 27. When the poppet valve 2 is closed, the upper end of the lower compression ring 24 is located adjacent to the lower end of the upper compression ring 23. The lower compression ring 24 is provided between the oil ring 22 and the upper compression ring 23. The oil ring 22 is provided on the cylindrical side face of the member.

When the valve cover 7 moves, the lower compression ring 24 also moves. The moving lower compression ring 24 transfers the residual oil which is not removed by the oil ring to the lower end of the upper compression ring 23. The upper compression ring 23 is thus lubricated.

A spray hole of oil is provided between the position of the lower compression ring 24 when the cam shifts the valve cover 7 at the maximum and the position of the oil ring 22 when the poppet valve 2 is closed. Thus, the amount of oil which the lower compression ring 24 transfers increases. 

1. A piston engine with a member to cover a bottom face of a valve head of a poppet valve, comprising: a combustion chamber defined between a piston and a cylinder head, in which the combustion chamber further extends outside a main cylinder; an inner wall of the combustion chamber, comprising a first part and a second part, the first part being a part facing with an upper face of the piston provided inside the main cylinder, the second part being an extended part outside the main cylinder a sub cylinder provided outside the main cylinder; the poppet valve provided on the second part, the poppet valve being provided with a second drive unit to drive a stem of the poppet valve, in which a gas passes through a gap between the poppet valve and a second valve sheet of the poppet valve when the poppet valve is open; the member to cover the bottom face of the valve head of the poppet valve, in which the member reciprocates in the sub cylinder and comprises a cylindrical side face, in which the valve head is located between the second valve sheet and the member; a means to make the second valve sheet, the valve head and the member contact closely one another, in which the second drive unit and the means drive the poppet valve and the member integrally, in which the member abuts the bottom face of the poppet valve; a compression ring provided at a position wedged between an inner wall of the sub cylinder and the cylindrical side face of the member; and an overhead valve provided on the first part, in which a gas passes through the a gap between the overhead valve and a first valve sheet of the overhead valve when the overhead valve is open, in which the overhead valve is provided with a first spring and a first drive unit, wherein a combination of the overhead valve and the poppet valve includes at least one intake valve and one exhaust valve, and the total number of the overhead valve and the poppet valve is not less than
 3. 2. A piston engine with a member to cover a bottom face of a valve head of a poppet valve, comprising: a combustion chamber defined between a piston and a cylinder head, in which the combustion chamber further extends outside a main cylinder; an inner wall of the combustion chamber, comprising a first part and a second part, the first part being a part facing with an upper face of the piston provided inside the main cylinder, the second part being an extended part outside the main cylinder a sub cylinder provided outside the main cylinder; the poppet valve provided on the second part, the poppet valve being provided with a second drive unit to drive a stem of the poppet valve; the member to cover the bottom face of the valve head of the poppet valve, in which the member reciprocates in the sub cylinder and comprises a cylindrical side face, in which the valve head is located between a second valve sheet of the poppet valve and the member; a means to make the second valve sheet, the valve head and the member contact closely one another, in which the second drive unit and the means drive the poppet valve and the member integrally, in which the member abuts the bottom face of the poppet valve; a compression ring provided at a position wedged between an inner wall of the sub cylinder and the cylindrical side face of the member; and an overhead valve provided on the first part, in which a gas passes through the a gap between the overhead valve and a first valve sheet of the overhead valve when the overhead valve is open, in which the overhead valve is provided with a first spring and a first drive unit, wherein a combination of the overhead valve and the poppet valve includes at least one intake valve and one exhaust valve, a plurality of the poppet valve are provided on the second part, all of the plurality of poppet valves provided on the second part being exhaust poppet valves, and at least one of the overhead valve provided on the first part is an intake valve.
 3. The piston engine with the member according to claim 1, wherein a plurality of the poppet valve is provided on the second part, all of the plurality of poppet valves provided on the second part being intake poppet valves, and at least one of the overhead valve provided on the first part is an exhaust valve.
 4. A piston engine with a member to cover a bottom face of a valve head of a poppet valve, comprising: a combustion chamber defined between a piston and a cylinder head, in which the combustion chamber further extends outside a main cylinder; an inner wall of the combustion chamber, comprising a first part and a second part, the first part being a part facing with an upper face of the piston provided inside the main cylinder, the second part being an extended part outside the main cylinder; a sub cylinder provided outside the main cylinder; the poppet valve provided on the second part, the poppet valve being provided with a second drive unit to drive a stem of the poppet valve, in which a gas passes through a gap between the poppet valve and a second valve sheet of the poppet valve when the poppet valve is open; the member to cover the bottom face of the valve head of the poppet valve, in which the member reciprocates in the sub cylinder and comprises a cylindrical side face, in which the valve head is located between the second valve sheet of the poppet valve and the member; a means to make the second valve sheet, the valve head and the member contact closely one another, in which the second drive unit and the means drive the poppet valve and the member integrally, in which the member abuts the bottom face of the poppet valve; a compression ring provided at a position between an inner wall of the sub cylinder and the cylindrical side face of the member; and at least one or more overhead valve provided on the first part, all of the overhead valve provided on the first part being an intake overhead valve, in which the overhead valve is provided with a first spring and a first drive unit, wherein the total number of the overhead valve and the poppet valve is not less than 3, and an exhaust poppet valve is provided on the second part.
 5. The piston engine with the member according to claim 1, wherein one end of the sub cylinder is located adjacent to the second valve sheet, a whole circumference of the cylindrical side face of the member adjacent to the poppet valve is sectioned into two half circumferences by a line which is perpendicular to a line connecting a central axis of the main cylinder and a central axis of the sub cylinder intersecting at the central axis of the sub cylinder, the two half circumferences are referred to as a first half circumference which is close to the central axis of the main cylinder and a second half circumference which is away from the central axis of the main cylinder, the cylindrical side face of the member adjacent to the poppet valve is sectioned into two half surrounding faces, the two half surrounding faces are a first half surrounding face having the first half circumference and a second half surrounding face having the second half circumference, a part adjacent to the second valve sheet of the sub cylinder faces with the second half surrounding face, a fixed wall, which is located outside the combustion chamber extended outside the main cylinder, is formed adjacent to an inner wall facing with the second half surrounding face of the sub cylinder, the sub cylinder comprises a opening in a vicinity of the one end of the sub cylinder, the piston engine further comprises: a first gas path provided between the second valve sheet and outside of the engine; and a second gas path which communicates an inner space of the main cylinder and the first gas path in a short distance when the poppet valve is open, the second gas path including the opening, and the opening faces with the first half surrounding face.
 6. The piston engine with the member according to claim 2, wherein one end of the sub cylinder is located adjacent to the second valve sheet, a whole circumference of the cylindrical side face of the member adjacent to the poppet valve is sectioned into two half circumferences by a line which is perpendicular to a line connecting a central axis of the main cylinder and a central axis of the sub cylinder intersecting at the central axis of the sub cylinder, the two half circumferences are referred to as a first half circumference which is close to the central axis of the main cylinder and a second half circumference which is away from the central axis of the main cylinder, the cylindrical side face of the member adjacent to the poppet valve is sectioned into two half surrounding faces, the two half surrounding faces are a first half surrounding face having the first half circumference and a second half surrounding face having the second half circumference, a part adjacent to the second valve sheet of the sub cylinder faces with the second half surrounding face, a fixed wall, which is located outside the combustion chamber extended outside the main cylinder, is formed adjacent to an inner wall facing with the second half surrounding face of the sub cylinder, the sub cylinder comprises a opening in a vicinity of the one end of the sub cylinder, the piston engine further comprises: a first gas path provided between the second valve sheet and outside of the engine; and a second gas path which communicates an inner space of the main cylinder and the first gas path in a short distance when the poppet valve is open, the second gas path including the opening, and the opening faces with the first half surrounding face.
 7. The piston engine with the member according to claim 3, wherein one end of the sub cylinder is located adjacent to the second valve sheet, a whole circumference of the cylindrical side face of the member adjacent to the poppet valve is sectioned into two half circumferences by a line which is perpendicular to a line connecting a central axis of the main cylinder and a central axis of the sub cylinder intersecting at the central axis of the sub cylinder, the two half circumferences are referred to as a first half circumference which is close to the central axis of the main cylinder and a second half circumference which is away from the central axis of the main cylinder, the cylindrical side face of the member adjacent to the poppet valve is sectioned into two half surrounding faces, the two half surrounding faces are a first half surrounding face having the first half circumference and a second half surrounding face having the second half circumference, a part adjacent to the second valve sheet of the sub cylinder faces with the second half surrounding face, a fixed wall, which is located outside the combustion chamber extended outside the main cylinder, is formed adjacent to an inner wall facing with the second half surrounding face of the sub cylinder, the sub cylinder comprises a opening in a vicinity of the one end of the sub cylinder, the piston engine further comprises: a first gas path provided between the second valve sheet and outside of the engine; and a second gas path which communicates an inner space of the main cylinder and the first gas path in a short distance when the poppet valve is open, the second gas path including the opening, and the opening faces with the first half surrounding face.
 8. The piston engine with the member according to claim 4, wherein one end of the sub cylinder is located adjacent to the second valve sheet, a whole circumference of the cylindrical side face of the member adjacent to the poppet valve is sectioned into two half circumferences by a line which is perpendicular to a line connecting a central axis of the main cylinder and a central axis of the sub cylinder intersecting at the central axis of the sub cylinder, the two half circumferences are referred to as a first half circumference which is close to the central axis of the main cylinder and a second half circumference which is away from the central axis of the main cylinder, the cylindrical side face of the member adjacent to the poppet valve is sectioned into two half surrounding faces, the two half surrounding faces are a first half surrounding face having the first half circumference and a second half surrounding face having the second half circumference, a part adjacent to the second valve sheet of the sub cylinder faces with the second half surrounding face, a fixed wall, which is located outside the combustion chamber extended outside the main cylinder, is formed adjacent to an inner wall facing with the second half surrounding face of the sub cylinder, the sub cylinder comprises a opening in a vicinity of the one end of the sub cylinder, the piston engine further comprises: a first gas path provided between the second valve sheet and outside of the engine; and a second gas path which communicates an inner space of the main cylinder and the first gas path in a short distance when the poppet valve is open, the second gas path including the opening, and the opening faces with the first half surrounding face.
 9. The piston engine with the member according to claim 1, wherein a stroke length of the piston is not shorter than a diameter of the piston.
 10. The piston engine with the member according to claim 2, wherein a stroke length of the piston is not shorter than a diameter of the piston.
 11. The piston engine with the member according to claim 3, wherein a stroke length of the piston is not shorter than a diameter of the piston.
 12. The piston engine with the member according to claim 4, wherein a stroke length of the piston is not shorter than a diameter of the piston.
 13. The piston engine with the member according to claim 5, wherein a stroke length of the piston is not shorter than a diameter of the piston.
 14. The piston engine with the member according to claim 6, wherein a stroke length of the piston is not shorter than a diameter of the piston.
 15. The piston engine with the member according to claim 7, wherein a stroke length of the piston is not shorter than a diameter of the piston.
 16. The piston engine with the member according to claim 8, wherein a stroke length of the piston is not shorter than a diameter of the piston.
 17. The piston engine with the member according to claim 1, further comprising: a spray valve to spray oil toward a back face of a part adjacent to the poppet valve of the member; and a third spring abutting the back face.
 18. The piston engine with the member according to claim 2, further comprising: a spray valve to spray oil toward a back face of a part adjacent to the poppet valve of the member; and a third spring abutting the back face.
 19. The piston engine with the member according to claim 3, further comprising: a spray valve to spray oil toward a back face of a part adjacent to the poppet valve of the member; and a third spring abutting the back face.
 20. The piston engine with the member according to claim 4, further comprising: a spray valve to spray oil toward a back face of a part adjacent to the poppet valve of the member; and a third spring abutting the back face.
 21. The piston engine with the member according to claim 5, further comprising: a spray valve to spray oil toward a back face of a part adjacent to the poppet valve of the member; and a third spring abutting the back face.
 22. The piston engine with the member according to claim 6, further comprising: a spray valve to spray oil toward a back face of a part adjacent to the poppet valve of the member; and a third spring abutting the back face.
 23. The piston engine with the member according to claim 7, further comprising: a spray valve to spray oil toward a back face of a part adjacent to the poppet valve of the member; and a third spring abutting the back face.
 24. The piston engine with the member according to claim 8, further comprising: a spray valve to spray oil toward a back face of a part adjacent to the poppet valve of the member; and a third spring abutting the back face.
 25. The piston engine with the member according to claim 1, wherein the sub cylinder comprises a groove for the compression ring, and the compression ring is disposed on the groove.
 26. The piston engine with the member according to claim 2, wherein the sub cylinder comprises a groove for the compression ring, and the compression ring is disposed on the groove.
 27. The piston engine according to claim 4, wherein the sub cylinder comprises a groove for the compression ring, and the compression ring is disposed on the groove.
 28. The piston engine with the member according to claim 1, wherein a face contacting with the poppet valve of the member is a convex curve, a face contacting with the member of the poppet valve is a concave curve, and the two faces have a same curvature, the member and the poppet valve are not integrally formed, and the member and the valve head of the poppet valve contact with each other.
 29. The piston engine with the member according to claim 5, wherein a face contacting with the poppet valve of the member is a convex curve, a face contacting with the member of the poppet valve is a concave curve, and the two faces have a same curvature, the member and the poppet valve are not integrally formed, and the member and the valve head of the poppet valve contact with each other.
 30. The piston engine with the member according to claim 6 wherein the compression ring comprises: an upper compression ring provided on an inner wall of the sub cylinder near the combustion chamber; and a lower compression ring provided on the cylindrical side wall of the member, wherein the upper compression ring is provided between the lower compression ring and the combustion chamber, an upper end of the lower compression ring is located adjacent to a lower end of the upper compression ring when the poppet valve is closed, the piston engine further comprises a oil ring provided on the cylindrical side face of the member, and the lower compression ring is provided between the oil ring and the upper compression ring.
 31. The piston engine with the member according to claim 7 wherein the compression ring comprises: an upper compression ring provided on an inner wall of the sub cylinder near the combustion chamber; and a lower compression ring provided on the cylindrical side wall of the member, wherein the upper compression ring is provided between the lower compression ring and the combustion chamber, an upper end of the lower compression ring is located adjacent to a lower end of the upper compression ring when the poppet valve is closed, the piston engine further comprises a oil ring provided on the cylindrical side face of the member, and the lower compression ring is provided between the oil ring and the upper compression ring.
 32. The piston engine with the member according to claim 8 wherein the compression ring comprises: an upper compression ring provided on an inner wall of the sub cylinder near the combustion chamber; and a lower compression ring provided on the cylindrical side wall of the member, wherein the upper compression ring is provided between the lower compression ring and the combustion chamber, an upper end of the lower compression ring is located adjacent to a lower end of the upper compression ring when the poppet valve is closed, the piston engine further comprises a oil ring provided on the cylindrical side face of the member, and the lower compression ring is provided between the oil ring and the upper compression ring.
 33. The piston engine with the member according to claims 1, wherein the means is a device to bias the member toward the second valve sheet, the device to bias the member toward the second valve sheet is a third spring abutting the member, and the third spring does not face with a space of the combustion chamber.
 34. The piston engine with the member according to claims 5, wherein the means is a device to bias the member toward the second valve sheet, the device to bias the member toward the second valve sheet is a third spring abutting the member, and the third spring does not face with a space of the combustion chamber.
 35. The piston engine with the member according to claims 6, wherein the means is a device to bias the member toward the second valve sheet, the device to bias the member toward the second valve sheet is a third spring abutting the member, and the third spring does not face with a space of the combustion chamber.
 36. The piston engine with the member according to claims 7, wherein the means is a device to bias the member toward the second valve sheet, the device to bias the member toward the second valve sheet is a third spring abutting the member, and the third spring does not face with a space of the combustion chamber.
 37. The piston engine with the member according to claims 8, wherein the means is a device to bias the member toward the second valve sheet, the device to bias the member toward the second valve sheet is a third spring abutting the member, and the third spring does not face with a space of the combustion chamber. 